α-MSH-antagonist dipeptide conjugates

ABSTRACT

The invention relates to a dipeptide conjugate having general formula I, AA2-AA1-NH 2 , wherein A represent the radical corresponding to a monocarboxylic acid with general formula II, HOOC—R, in which: R represents a linear or branched aliphatic radical at C 1 -C 24 , which is optionally substituted by a hydroxyl group and which can comprise one or more unsaturations, preferably between 1 and 6 unsaturations, and/or which can comprise a phenyl group or lipoic acid or the reduced form thereof, dihydrolipoic acid or N-lipoyllysine; and AA1 and AA2 represent identical or different amino acids which are selected from the group containing Ala, Asn, Cys, Gln, Gly, Ile, Leu, Met, Phe, Pro, Ser, Thr, Trp, Tyr, Val, Asp, Glu, Arg, His, Lys, Orn, Dap, Dab, the corresponding homo-amino acids and the corresponding beta-amino acids in the form of enantiomers or diastereoisomers and mixtures thereof, including racemic mixtures.

This application is a National Stage application of PCT/FR2005/001164, filed May 10, 2005, which claims priority from French patent applications FR 0405069, filed May 11, 2004, and 0411279, filed Oct. 22, 2004. The entire contents of each of the aforementioned applications are incorporated herein by reference.

This invention relates to new alpha-MSH antagonist dipeptide conjugates and their use as a medicine or as a depigmenting agent.

Melanocortine receptors belong to the superfamily of seven transmembrane receptors coupled to protein G and they stimulate the AMPc signal transduction channel (Cone et al. Recent Prog. Horm. Res. 1996, 51, pages 287-317). The melanocortine system is involved in many physiological channels including pigmentation, inflammation, the erectile function, food behavior, energy homeostasis, weight homeostasis and the exocrine glands function. The endogenic agonist ligands for these melanocortine receptors are derived by post-translational modification of the transcript of the proopiomelanocortine gene, that during differential treatment causes generation of α, β and γ hormones stimulating melanocytes (MSH) and corticotrophine (ACTH). Subtypes of melanocortine receptors are activated by all endogenic melanocortine peptides, except for the melanocortine MC₂ receptor that is only stimulated by corticotrophine. The family of melanocortine receptors also has two endogenic antagonists, namely agouti and protein related to agouti (AGRP) (Lu et al. Nature 1994, 371, pages 799-802, Ollmann et al., Science 1997, pages 135-138, Shulter et al., Genes Dev. 1997, 11, pages 593-602) that are the only known antagonists discovered at the moment existing in the natural state of these receptors coupled with protein G. These are polypeptides of 132 and 49 amino acid residues respectively. The most studied melanocortine receptor ligands are MC, receptor ligands of melanocortine of the skin that are involved in pigmentation and coloring of animal hair coat (Hruby et al. Ann. N.Y. Acad. Sci. 1993, 680, pages 51-63; Lerner et al. Nature 1961, pages 189, 176; Mountjoy et al. Science 1992, 257, pages 1248-1251).

Nonapepdide 153 N-6 (Jayawickreme et al., J. Biol. Chem. 1994, 269, pages 29846-29854) (H-Met-Pro-D-Phe-Arg-d-Trp-Phe-Lys-Pro-Val-NH₂: Ki=11 nM) is a synthetic antagonist of the receptor MC₁. However, this compound has a high molecular weight and therefore a very limited therapeutic or cosmetic activity. Its size makes it difficult to optimize and its bioavailability is limited. It is also expensive and difficult to prepare.

Tripeptide D-Trp-Arg-Leu-NH₂ (Proc. Natl. Acad. Sci. (1995), 92, pages 2894-2898) also has an antagonist activity. However, it contains tryptophan that is an unstable amino acid and therefore can cause stability problems during storage.

Patent EP 1 174 437 describes di- or tripeptides comprising a naphthyl group and in particular a naphthylalanyl group. However, the presence of the naphthyl group increases the fabrication price of the product. Furthermore in some countries such as Japan, unnatural amino acid based peptides cannot be sold for cosmetic applications. Furthermore, no dipeptide activity is indicated.

Surprisingly, the inventors discovered that dipeptides conjugated at the C-terminal with carboxylic acids have an antagonist activity of the MSH alpha. These antagonists have a very low molecular weight and are therefore easy to optimize, they have good bioavailability and are very easy to prepare.

Therefore, this invention relates to a dipeptide conjugate with general formula I below: A-AA2-AA1-NH₂  I in which

A represents the radical corresponding to a monocarboxylic acid with the following general formula II: HOOC—R  II in which R represents

a linear or branched aliphatic radical in C₁-C₂₄, optionally substituted by a hydroxyl group, which can comprise one or more unsaturations, preferably between 1 and 6 unsaturations, and/or which can comprise a phenyl group,

or lipoic acid or the reduced form thereof, dihydrolipoic acid or N-lipoyllysine.

AA1 and AA2 represent identical or different amino acids chosen from the group consisting of Ala, Asn, Cys, Gln, Gly, Ile, Leu, Met, Phe, Pro, Ser, Thr, Trp, Tyr, Val, Asp, Glu, Arg, H is, Lys, Orn, Dap, Dab, the corresponding homo-amino acids and the corresponding beta-amino acids,

in the form of enantiomers or diastereoisomers and mixtures thereof including racemic mixtures.

Amino acids in the dipeptide conjugate with formula (I) may have a D, L or DL configuration if it is not specified otherwise.

Thus, dipeptide conjugates with formula (I) may comprise one or more asymmetric carbon atoms. Therefore, they may exist in the form of enantiomers or diastereoisomers. The invention includes these enantiomers, diastereoisomers and mixtures thereof, including racemic mixtures.

Within the framework of this invention, the following abbreviations have the following meanings:

-   -   Ala, Alanine,     -   Asn, Asparagine,     -   Cys, Cystein,     -   Gln, Glutamine,     -   Gly, Glycine,     -   Ile, Isoleucine,     -   Leu, Leucine,     -   Met, Methionine,     -   Phe, Phenylalanine or similar, particularly a halogenated         derivative, and particularly para-fluoro-Phe, Homo-Phe,         para-nitro-Phe or phenylglycine     -   Pro, Proline,     -   Ser, Serine,     -   Thr, Threonine,     -   Trp, Tryptophan,     -   Tyr, Tyrosine,     -   Val, Valine,     -   Asp, Aspartic acid,     -   Glu, Glutamic acid,     -   Arg, Arginine,     -   H is, Histidine,     -   Lys, Lysine,     -   Orn, Ornithine,     -   Dap, Diaminopropionic acid,     -   Dab, Diaminobutyric acid.

Note also that the dipeptide conjugates mentioned above according to this invention are obtained in the terminal form NH₂ (in other words they present an amide function).

Dipeptide conjugates according to this invention are bonded to acid with formula II in the form of salts or esters. The conjugations according to this invention may be made by making the acid function of the amino acid react with the acid function of the formula II acid, or it is even possible to take advantage of the presence of a hydroxyl function on the formula II acid.

This invention relates to all these conjugations and non-functional conjugates. Conjugations may be physical or chemical.

Advantageously, at least one of the amino acids AA2 or AA1, and advantageously both of them, represent a basic amino acid, advantageously selected from the group consisting of Arg, H is, Dap, Dab, Orn or Lys, advantageously it will be Arg.

Advantageously, AA2 represents a basic amino acid advantageously selected from the group consisting of Arg, H is, Lys, Orn, Dap, Dab, advantageously it is Arg.

Advantageously, AA1 and/or AA2 do not represent Trp.

Advantageously, AA1 and/or AA2 do not represent Cys.

Advantageously, at least one of the amino acids AA1 or AA2 is selected from the group consisting of Ser and Pro.

Advantageously AA1 represents Pro.

Advantageously AA2 represents Ser.

Advantageously, the acid with formula (II) is a polyunsaturated fatty acid, in other words it comprises between 1 and 6 unsaturations. Even more advantageously, it is an omega-3 acid.

Among these omega-3 acids, there is particularly α-linolenic acid, cervonic acid, timnodonic acid and pinolenic acid. Cervonic, timnodonic and pinolenic acids are also known under the names 4,7,10,13,16,19-docosahexaenoic acid (DHA), 5,8,11,14,17-eicosapentaenoic acid (EPA) and 5,9,12-octodecatrienoic acid, respectively.

When A represents a monocarboxylic acid radical with general formula (II), it may advantageously be selected from among acetic acid, myristic acid, palmitic acid, hydroxydecenoic and decenoic acid, and particularly trans-10-hydroxy-Δ2-decenoic acid and trans-oxo-9-decene-2-oic acid.

Advantageously, acid with formula (II) is an acid selected from among lipoic acid (Lip) or its reduced form dihydrolipoic acid, N-lipoyllysine or phenylbutyric acid (Pbu).

Advantageously, A represents the radical corresponding to palmitic acid (Palm).

The dipeptide conjugates of the invention include the dipeptide conjugates selected from among the group consisting of:

a) A-Arg-His-NH₂,

b) A-Arg-Arg-NH₂,

c) A-Arg-Pro-NH₂,

d) A-Arg-Lys-NH₂,

e) A-Ser-Pro-NH₂,

f) A-DPhe-Arg-NH₂,

in which the definition of A is as given above.

In particular, the dipeptide conjugates in the invention may be selected from among the group consisting of

39) Palm-Arg-His-NH₂,

41) Palm-Arg-Arg-NH₂,

49) Palm-Arg-Pro-NH₂,

50) Palm-Arg-Lys-NH₂,

125) Palm-Ser-Pro-NH₂,

269) Palm-DPhe-Arg-NH₂,

362) Pbu-DPhe-Arg-NH₂,

363) Lip-DPhe-Arg-NH₂

Dipeptide conjugates according to this invention may be obtained either advantageously by classical chemical synthesis, or by enzymatic synthesis using any processes known to those skilled in the art.

This invention also relates to a cosmetic, dermatological or pharmaceutical composition or a food supplement comprising a dipeptide conjugate according to this invention and possibly a cosmetically or pharmaceutically acceptable excipient.

Dipeptide conjugates can be administered for their cosmetic or pharmaceutical use by topical route. They can also be used orally in food supplements, in other words in the nutraceutical domain.

Dipeptide conjugates according to the invention are preferably administered topically.

The cosmetic, pharmaceutical or dermatological composition according to this invention intended for topical administration may be presented in forms that are normally known for this type of administration, in other words particularly lotions, foams, gels, dispersions, sprays, serums, masks, body milk, pomades, solutions, emulsions, gels, or creams for example with excipients particularly for skin penetration in order to improve the properties and accessibility of the active ingredient. These compositions usually also contain the dipeptide conjugate according to this invention and usually also a physiologically acceptable medium, usually based on water or solvent, for example alcohols, ethers or glycols. They can also contain surface active agents, preservatives, stabilizers, emulsifiers, thickeners, other active constituents leading to a complementary or possibly synergic effect, trace elements, essential oils, perfumes, coloring agents, collagen, chemical or mineral filters, moisturizers or thermal water.

In the composition according to this invention, the dipeptide conjugate according to the invention may be present at a concentration of between 10⁻⁸ M and 10⁻³ M, advantageously between 10⁻⁷ M and 10⁻⁵ M.

This invention also relates to a dipeptide conjugate according to this invention or a pharmaceutical composition according to this invention for its use as a medicine, advantageously designed to prevent, improve or treat immunitary abnormalities, immunodeficiency, to regulate the body weight by controlling the appetite, to treat disorders of the central nervous system, to regulate satiety, to treat anorexia or some skin cancers.

This invention also relates to the use of a cosmetic composition according to this invention as a depigmenting agent to lighten or whiten the epidermis, to eliminate skin spots, particularly age spots or freckles, or to prevent pigmentation of the epidermis.

Finally, this invention relates to a cosmetic treatment process to lighten, depigment or whiten the epidermis, to eliminate skin spots and particularly age spots or freckles, or prevent pigmentation of the epidermis including application of a cosmetic composition according to this invention to the skin.

The following examples are given for non-limitative guidance.

EXAMPLE 1 Preparation of 361 Dipeptides According to the Invention

A bank of acylated dipeptides with 361 members was synthesized using SynPhase™ Lanterns and a “split and pool” strategy for color marking as described in the article by Feliu et al. (J. Comb. Chem., 2003, 5, pages 256-361).

Thus, these 361 compounds were synthesized on series D SynPhase™ Lanterns with Rink amide PS resin using the standard Fmoc (9-fluorenyl-methoxycarbonyl) synthesis strategy in the solid phase using a Multipin 96 arrangement format. Component blocks AA1 and AA2 were selected from a chemical assembly of 19 D and L amino acids including several types of lateral chains (alkyl, aromatic, acid, voluminous, basic) to produce 19×19=361 combinations.

The following chemical products were used:

Amino acids protected at the N-terminal end by an α-Fmoc, Fmoc-Ala-OH, Fmoc-D-Ala-OH, Fmoc-Arg(Pbf)-OH, Fmoc-D-Arg-(Pbf)-OH, Fmoc-His(Trt)-OH, Fmoc-D-His(Trt)-OH, Fmoc-Lys(Boc)-OH, Fmoc-Phe-OH, Fmoc-D-Phe-OH, Fmoc-Trp(Boc)-OH, Fmoc-D-Trp(Boc)-OH, Fmoc-Met-OH, Fmoc-Glu(OtBu)-OH, Fmoc-Ser(tBu)-OH, Fmoc-Leu-OH, Fmoc-Tyr(tBu)-OH, Fmoc-Gly-OH, Fmoc-Pro-OH, or Fmoc-Asn(trt)-OH group, were purchased from SENN chemicals and Advanced Chemtech.

The coupling agent, HBTU (hexafluorophosphate of 2-(1-H-benzotriazol-1-yl)-1,1,3,3-tetramethyl-uronium), was purchased from SENN chemicals.

N,N-dimethylformamide (DMF), dichloromethane, methanol, acetonitrile, ethyl ether, trifluoroacetic acid (TFA), piperidine were purchased from Riedel de Haen, Carlo Erba or Acros organics and used without purification.

N,N-diisopropylethylamine (DIEA), triisopropyl-silane, palmitic acid were purchased from Aldrich or Avocado. All reagents and chemical products were of analytic quality and they were used without any other purification.

D series Synphase Polystyrene Rink amide Lanterns were supplied by Mimotopes, Pty.

The standard procedure for manufacturing these dipeptides includes the following steps:

1—Fmoc Standard Deprotection Protocol

Fmoc deprotection steps were done by immersing lanterns immobilized on a support of 96 rods in a mix of dimethylsulfoxide (DMF)/piperidine (80/20, v/v) for 30 minutes. Rectangular polypropylene receptacles of the same size as a standard plate with 96 wells were used. The excess deprotection solution was simply eliminated by stirring the rod support vigorously.

2—Standard Washing Protocol

After the coupling or deprotection step, washing steps were carried out by dipping the lanterns arranged in a Multipin format into polypropylene receptacles containing DMF (3×5 min), methanol (2×5 min) and dichloromethane (DCM) (1×5 min), all in sequence. The lanterns were dried in air for 5 minutes under a vapor hood after the last washing with DCM.

3—Standard Coupling Protocol

0.4 M solutions of each Fmoc amino acid, HBTU and DIEA were prepared in DMF and were kept at 4° C. throughout the synthesis. 200 μl of amino acid solution were distributed in plates with 96 deep wells. 200 μl of DIEA solution and 200 μl of HBTU solution were then added and finally, the support of the rods supporting the lanterns was adapted to the deep wells plate for 2 hours.

4—Cleavage

500 μl of TFA/water/triisopropylsilane (95/2.5/2.5, v/v/v) solution was distributed in individual polypropylene tubes arranged in Micronic plates with 96 wells. Cleavage was done for 3 hours. The cleavage cocktail was concentrated directly from plates using a Jouan RC1010 vacuum centrifuge. Compounds were precipitated with dry diethyl ether, and were centrifuged and settled one by one. Precipitation, centrifuging and settlement operations were repeated twice. 500 μl of acetonitrile/water (50/50, v/v) containing 0.1% of TFA were distributed in each tube to solubilize the samples. The samples were then frozen at −80° C. and freeze dried. This operation was repeated twice to completely eliminate the triisopropylsilane purification group.

5—Preparation and Analysis of Samples

Complete banks and simple re-synthesized peptides were analyzed by CLHP in inverse phase and CL/SM. 500 μl of acetonitrile/water (50/50, v/v) containing 0.1% of TFA were distributed on the freeze-dried compounds. 10 μl of each tube was sampled for analysis of CLHP and CL/SM ESI+.

The CLHP analyses were carried out on a CLHP Waters Alliance 2690 system and a Waters 996 photodiode strip detector and a 50×4.6 mm Merck Chromolith Speed ROD C18 column. A flow rate of 5 ml/min and a gradient from 100% of B to 100% of C was used over 3 minutes (Eluant B, water/0.1% of TFA; Eluant C, acetronitrile/0.1% of TFA). Estimates of the purity are based on the percent of the area of peaks detected at 214 nm.

The CL/SM system was composed of a Waters Alliance 2690 CLHP coupled to a Micromass Platform II spectrometer (ionization by electronebulization mode; ESI+). All analyses were done using a 2.1×30 mm Waters Symmetry C18 column, 3.5 μm. A 600 μl/min flow rate and a gradient from 100% of B to 100% of C over 3 minutes were used (Eluant B, water/0.1% of TFA; Eluant C, acetonitrile/0.1% of TFA).

Mass spectra by positive ionic electronebulization were acquired at a solvent flow rate of 100 ml/min. Nitrogen was used both for the nebulizing gas and for the drying gas. Data were acquired in read mode m/z 400 to 1400 at intervals of 0.1^(−s); 10 readings were added to produce the final spectrum.

The molecular weights of all compounds were calculated using mono-isotopic masses (C=12.000, H=1.007, N=14.003, O=15.994, S=31.972).

Table 1 below contains the analysis results.

TABLE 1 Analytic results of the Palm-dipeptides bank Dipeptide conjugate number according to the Sequence % Molecular invention A AA2 AA1 purity weight  1 Palm His His NH₂ 97 529.3   2 Palm His Phe NH₂ 100  539.4   3 Palm His Arg NH₂ 100  548.4   4 Palm His Trp NH₂ 89 578.4   5 Palm His Glu NH₂ 100  521.3   6 Palm His Ala NH₂ 100  463.3   7 Palm His Ser NH₂ 100  479.3   8 Palm His Leu NH₂ 100  505.4   9 Palm His Tyr NH₂ 100  555.3   10 Palm His Gly NH₂ 96 449.3   11 Palm His Pro NH₂ 100  489.3   12 Palm His Lys NH₂ 100  520.4   13 Palm His Asn NH₂ 100  506.3   14 Palm His Met NH₂ 88 523.3   15 Palm His DPhe NH₂ 81 539.4   16 Palm His DTrp NH₂ 88 578.4   17 Palm His DArg NH₂ 100  548.4   18 Palm His DHis NH₂ 97 529.3   19 Palm His DAla NH₂ 88 463.3   20 Palm Phe His NH₂ 100  539.4 

 22 Palm Phe Arg NH₂ 100  558.4   23 Palm Phe Trp NH₂ 100  588.4   24 Palm Phe Glu NH₂ 100  531.3   25 Palm Phe Ala NH₂ 100  473.3   26 Palm Phe Ser NH₂ 100  489.3 

 28 Palm Phe Tyr NH₂ 100  565.4   29 Palm Phe Gly NH₂ 100  459.3   30 Palm Phe Pro NH₂ 23 499.35  31 Palm Phe Lys NH₂ 100  530.4   32 Palm Phe Asn NH₂ 80 516.3   33 Palm Phe Met NH₂ 100  533.3   34 Palm Phe DPhe NH₂ 100  549.4 

 36 Palm Phe DArg NH₂ 100  558.4   37 Palm Phe DHis NH₂ 96 539.4   38 Palm Phe DAla NH₂ 100  473.3   39 Palm Arg His NH₂ 94 548.4   40 Palm Arg Phe NH₂ 100  558.4   41 Palm Arg Arg NH₂ 100  567.4   42 Palm Arg Trp NH₂ 95 597.4   43 Palm Arg Glu NH₂ 100  540.4   44 Palm Arg Ala NH₂ 94 482.4   45 Palm Arg Ser NH₂ 100  498.4   46 Palm Arg Leu NH₂ 100  524.4   47 Palm Arg Tyr NH₂ 93 574.4   48 Palm Arg Gly NH₂ 100  468.3   49 Palm Arg Pro NH₂ 87 508.4   50 Palm Arg Lys NH₂ 100  539.4   51 Palm Arg Asn NH₂ 91 525.4   52 Palm Arg Met NH₂ 100  542.4   53 Palm Arg DPhe NH₂ 100  558.4   54 Palm Arg DTrp NH₂ 60 597.4   55 Palm Arg DArg NH₂ 100  567.4   56 Palm Arg DHis NH₂ 100  548.4   57 Palm Arg DAla NH₂ 100  482.4   58 Palm Trp His NH₂ 93 578.4   59 Palm Trp Phe NH₂ 100  588.4   60 Palm Trp Arg NH₂ 100  597.4 

 62 Palm Trp Glu NH₂ 87 570.3   63 Palm Trp Ala NH₂ 89 512.3   64 Palm Trp Ser NH₂ 89 528.3 

 66 Palm Trp Tyr NH₂ 90 604.4   67 Palm Trp Gly NH₂ 90 498.3   68 Palm Trp Pro NH₂ 100  538.4   69 Palm Trp Lys NH₂ 99 569.4   70 Palm Trp Asn NH₂ 95 555.3   71 Palm Trp Met NH₂ 89 572.3 

 73 Palm Trp DTrp NH₂ 76 627.4   74 Palm Trp DArg NH₂ 93 597.4   75 Palm Trp DHis NH₂ 79 578.4   76 Palm Trp DAla NH₂ 100  512.3   77 Palm Glu His NH₂ 94 521.3   78 Palm Glu Phe NH₂ 100  531.3   79 Palm Glu Arg NH₂ 100  540.4   80 Palm Glu Trp NH₂ 82 570.3   81 Palm Glu Glu NH₂ 100  513.3   82 Palm Glu Ala NH₂ 100  455.3   83 Palm Glu Ser NH₂ 100  471.3   84 Palm Glu Leu NH₂ 100  497.4   85 Palm Glu Tyr NH₂ 100  547.3   86 Palm Glu Gly NH₂ 100  441.3   87 Palm Glu Pro NH₂ 10 481.32  88 Palm Glu Lys NH₂ 100  512.4   89 Palm Glu Asn NH₂  7 498.31  90 Palm Glu Met NH₂ 100  515.3   91 Palm Glu DPhe NH₂ 100  531.3 

 93 Palm Glu DArg NH₂ 100  540.4   94 Palm Glu DHis NH₂ 100  521.3   95 Palm Glu DAla NH₂ 100  455.3   96 Palm Ala His NH₂ 97 463.3   97 Palm Ala Phe NH₂ 94 473.3   98 Palm Ala Arg NH₂ 100  482.4   99 Palm Ala Trp NH₂ 98 512.3  100 Palm Ala Glu NH₂ 100  455.3  101 Palm Ala Ala NH₂ 100  397.3  102 Palm Ala Ser NH₂ 100  413.3  103 Palm Ala Leu NH₂ 100  439.3  104 Palm Ala Tyr NH₂ 100  489.3  105 Palm Ala Gly NH₂ 100  383.3  106 Palm Ala Pro NH₂ 100  423.3  107 Palm Ala Lys NH₂ 100  454.4  108 Palm Ala Asn NH₂ 100  440.3  109 Palm Ala Met NH₂ 100  457.3  110 Palm Ala DPhe NH₂ 100  473.3  111 Palm Ala DTrp NH₂ 96 512.3  112 Palm Ala DArg NH₂ 100  482.4  113 Palm Ala DHis NH₂ 84 463.3  114 Palm Ala DAla NH₂ 100  397.3  115 Palm Ser His NH₂ 95 479.3  116 Palm Ser Phe NH₂ 100  489.3  117 Palm Ser Arg NH₂ 100  498.4  118 Palm Ser Trp NH₂ 96 528.3  119 Palm Ser Glu NH₂ 100  471.3  120 Palm Ser Ala NH₂ 100  413.3  121 Palm Ser Ser NH₂ 100  429.3  122 Palm Ser Leu NH₂ 100  455.3  123 Palm Ser Tyr NH₂ 97 505.3  124 Palm Ser Gly NH₂ 100  399.3  125 Palm Ser Pro NH₂ 100  439.3  126 Palm Ser Lys NH₂ 100  470.4  127 Palm Ser Asn NH₂ 32 456.3  128 Palm Ser Met NH₂ 50 473.3  129 Palm Ser DPhe NH₂ 100  489.3  130 Palm Ser DTrp NH₂ 93 528.3  131 Palm Ser DArg NH₂  0 498.4  132 Palm Ser DHis NH₂ 91 479.3  133 Palm Ser DAla NH₂ 100  413.3  134 Palm Leu His NH₂ 92 505.4  135 Palm Leu Phe NH₂ 100  515.4  136 Palm Leu Arg NH₂ 100  524.4  137 Palm Leu Trp NH₂ 100  554.4  138 Palm Leu Glu NH₂ 100  497.4  139 Palm Leu Ala NH₂ 100  439.3  140 Palm Leu Ser NH₂ 100  455.3  141 Palm Leu Leu NH₂ 100  481.4  142 Palm Leu Tyr NH₂ 100  531.4  143 Palm Leu Gly NH₂ 100  425.3 

145 Palm Leu Lys NH₂ 100  496.4  146 Palm Leu Asn NH₂ 15 482.4  147 Palm Leu Met NH₂ 100  499.3  148 Palm Leu DPhe NH₂ 100  515.4  149 Palm Leu DTrp NH₂ 87 554.4  150 Palm Leu DArg NH₂ 100  524.4  151 Palm Leu DHis NH₂ 86 505.4  152 Palm Leu DAla NH₂ 100  439.3  153 Palm Tyr His NH₂ 96 555.3 

155 Palm Tyr Arg NH₂ 87 574.4  156 Palm Tyr Trp NH₂ 78 604.4  157 Palm Tyr Glu NH₂ 100  547.3  158 Palm Tyr Ala NH₂ 100  489.3  159 Palm Tyr Ser NH₂ 100  505.3  160 Palm Tyr Leu NH₂ 100  531.4  161 Palm Tyr Tyr NH₂ 98 581.4  162 Palm Tyr Gly NH₂ 100  475.3  163 Palm Tyr Pro NH₂ 93 515.3  164 Palm Tyr Lys NH₂ 100  546.4  165 Palm Tyr Asn NH₂ 100  532.3 

167 Palm Tyr DPhe NH₂ 87 565.4 

169 Palm Tyr DArg NH₂ 90 574.4  170 Palm Tyr DHis NH₂ 92 555.3  171 Palm Tyr DAla NH₂ 100  489.3  172 Palm Gly His NH₂ 81 449.3  173 Palm Gly Phe NH₂ 100  459.3  174 Palm Gly Arg NH₂ 100  468.3  175 Palm Gly Trp NH₂ 95 498.3  176 Palm Gly Glu NH₂ 100  441.3  177 Palm Gly Ala NH₂ 100  383.3  178 Palm Gly Ser NH₂ 100  399.3 

180 Palm Gly Tyr NH₂ 100  475.3  181 Palm Gly Gly NH₂ 100  369.3  182 Palm Gly Pro NH₂ 100  409.3  183 Palm Gly Lys NH₂ 81 440.3  184 Palm Gly Asn NH₂ 57 426.3  185 Palm Gly Met NH₂ 100  443.3  186 Palm Gly DPhe NH₂ 100  459.3  187 Palm Gly DTrp NH₂ 68 498.3  188 Palm Gly DArg NH₂ 100  468.3  189 Palm Gly DHis NH₂ 90 449.3  190 Palm Gly DAla NH₂ 100  383.3  191 Palm Pro His NH₂ 97 489.34 192 Palm Pro Phe NH₂ 97 499.35

197 Palm Pro Ser NH₂ 99 439.31 198 Palm Pro Leu NH₂ 72 465.36 199 Palm Pro Tyr NH₂ 98 515.34 200 Palm Pro Gly NH₂ 24 409.30 201 Palm Pro Pro NH₂ 78 449.33 202 Palm Pro Lys NH₂ 93 480.37 203 Palm Pro Asn NH₂ 97 466.32 204 Palm Pro Met NH₂ 97 483.32 205 Palm Pro DPhe NH₂ 22 499.35 206 Palm Pro DTrp NH₂ 96 538.36 207 Palm Pro DArg NH₂ 37 508.38 208 Palm Pro DHis NH₂ 73 489.34 209 Palm Pro DAla NH₂ 59 423.32 210 Palm Lys His NH₂ 92 520.38

212 Palm Lys Arg NH₂ 73 539.42 213 Palm Lys Trp NH₂ 92 569.40 214 Palm Lys Glu NH₂ 90 512.36 215 Palm Lys Ala NH₂ 87 454.36 216 Palm Lys Ser NH₂ 86 470.35 217 Palm Lys Leu NH₂ 80 496.40 218 Palm Lys Tyr NH₂ 97 546.38 219 Palm Lys Gly NH₂ 89 440.34 220 Palm Lys Pro NH₂ 21 480.37 221 Palm Lys Lys NH₂ 96 511.41

223 Palm Lys Met NH₂ 89 514.36 224 Palm Lys DPhe NH₂ 95 530.39 225 Palm Lys DTrp NH₂ 92 569.40 226 Palm Lys DArg NH₂ 94 539.42 227 Palm Lys DHis NH₂ 94 520.38 228 Palm Lys DAla NH₂ 83 454.36 229 Palm Asn His NH₂ 28 506.33

231 Palm Asn Arg NH₂ 42 525.37 232 Palm Asn Trp NH₂ 88 555.35

234 Palm Asn Ala NH₂ 80 440.31

238 Palm Asn Gly NH₂ 32 426.30 239 Palm Asn Pro NH₂ 89 466.32 240 Palm Asn Lys NH₂ 30 497.36 241 Palm Asn Asn NH₂ 85 483.31 242 Palm Asn Met NH₂ 77 500.31 243 Palm Asn DPhe NH₂ 76 516.34 244 Palm Asn DTrp NH₂ 57 555.35

247 Palm Asn DAla NH₂ 95 440.31 248 Palm Met His NH₂ 85 523.33 249 Palm Met Phe NH₂ 84 533.33 250 Palm Met Arg NH₂ 76 542.37 251 Palm Met Trp NH₂ 85 572.34 252 Palm Met Glu NH₂ 87 515.31 253 Palm Met Ala NH₂ 99 457.31 254 Palm Met Ser NH₂ 55 473.30 255 Palm Met Leu NH₂ 78 499.35 256 Palm Met Tyr NH₂ 80 549.33 257 Palm Met Gly NH₂ 63 443.29 258 Palm Met Pro NH₂ 85 483.32 259 Palm Met Lys NH₂ 88 514.36 260 Palm Met Asn NH₂ 92 500.31 261 Palm Met Met NH₂ 85 517.31 262 Palm Met DPhe NH₂ 91 533.33 263 Palm Met DTrp NH₂ 78 572.34 264 Palm Met DArg NH₂ 57 542.37 265 Palm Met DHis NH₂ 86 523.33 266 Palm Met DAla NH₂ 31 457.31 267 Palm DPhe His NH₂ 95 539.35 268 Palm DPhe Phe NH₂ 76 549.36 269 Palm DPhe Arg NH₂ 85 558.39 270 Palm DPhe Trp NH₂ 70 588.37 271 Palm DPhe Glu NH₂ 33 531.34 272 Palm DPhe Ala NH₂ 97 473.33 273 Palm DPhe Ser NH₂ 83 489.33 274 Palm DPhe Leu NH₂ 79 515.38 275 Palm DPhe Tyr NH₂ 93 565.36 276 Palm DPhe Gly NH₂ 88 459.32 277 Palm DPhe Pro NH₂ 50 499.35 278 Palm DPhe Lys NH₂ 65 530.39 279 Palm DPhe Asn NH₂ 77 516.34 280 Palm DPhe Met NH₂ 97 533.33 281 Palm DPhe DPhe NH₂ 76 549.36 282 Palm DPhe DTrp NH₂ 87 588.37 283 Palm DPhe DArg NH₂ 92 558.39 284 Palm DPhe DHis NH₂ 96 539.35 285 Palm DPhe DAla NH₂ 78 473.33 286 Palm DTrp His NH₂ 69 578.36 287 Palm DTrp Phe NH₂ 82 578.36 288 Palm DTrp Arg NH₂ 79 588.37 289 Palm DTrp Trp NH₂ 46 597.40 290 Palm DTrp Glu NH₂ 71 627.38 291 Palm DTrp Ala NH₂ 60 570.35

293 Palm DTrp Leu NH₂ 37 528.34 294 Palm DTrp Tyr NH₂ 68 554.39 295 Palm DTrp Gly NH₂ 69 604.37 296 Palm DTrp Pro NH₂ 72 498.33 297 Palm DTrp Lys NH₂ 96 538.36 298 Palm DTrp Asn NH₂ 84 569.40 299 Palm DTrp Met NH₂ 60 555.35 300 Palm DTrp DPhe NH₂ 70 572.34 301 Palm DTrp DTrp NH₂ 52 588.37 302 Palm DTrp DArg NH₂ 86 627.38 303 Palm DTrp DHis NH₂ 95 597.40

306 Palm DArg Phe NH₂ 42 548.38 307 Palm DArg Arg NH₂ 60 558.39 308 Palm DArg Trp NH₂ 42 567.42 309 Palm DArg Glu NH₂ 73 597.40 310 Palm DArg Ala NH₂ 82 540.37 311 Palm DArg Ser NH₂ 74 482.36 312 Palm DArg Leu NH₂ 34 498.36 313 Palm DArg Tyr NH₂ 27 524.41 314 Palm DArg Gly NH₂ 32 574.39 315 Palm DArg Pro NH₂ 40 468.35

317 Palm DArg Asn NH₂ 40 539.42 318 Palm DArg Met NH₂  9 525.37 319 Palm DArg DPhe NH₂ 82 542.37 320 Palm DArg DTrp NH₂ 30 558.39 321 Palm DArg DArg NH₂ 20 597.40 322 Palm DArg DHis NH₂ 70 567.42 323 Palm DArg DAla NH₂ 83 548.38 324 Palm DHis His NH₂ 75 482.36 325 Palm DHis Phe NH₂ 66 529.35 326 Palm DHis Arg NH₂ 53 539.35 327 Palm DHis Trp NH₂ 69 548.38

329 Palm DHis Ala NH₂ 63 521.33 330 Palm DHis Ser NH₂ 47 463.32 331 Palm DHis Leu NH₂ 66 479.32 332 Palm DHis Tyr NH₂ 79 505.37 333 Palm DHis Gly NH₂ 89 555.35 334 Palm DHis Pro NH₂ 96 449.31 335 Palm DHis Lys NH₂ 90 489.34 336 Palm DHis Asn NH₂ 87 520.38 337 Palm DHis Met NH₂ 76 506.33 338 Palm DHis DPhe NH₂ 96 523.33 339 Palm DHis DTrp NH₂ 66 539.35

341 Palm DHis DHis NH₂ 84 548.38 342 Palm DHis DAla NH₂ 52 529.35 343 Palm DAla His NH₂ 70 463.32

345 Palm DAla Arg NH₂ 76 473.33 346 Palm DAla Trp NH₂ 84 482.36

348 Palm DAla Ala NH₂ 53 455.31 349 Palm DAla Ser NH₂ 11 397.30 350 Palm DAla Leu NH₂ 78 413.30 351 Palm DAla Tyr NH₂ 87 439.35

353 Palm DAla Pro NH₂ 17 383.29 354 Palm DAla Lys NH₂ 86 423.32 355 Palm DAla Asn NH₂ 94 454.36 356 Palm DAla Met NH₂ 10 440.31 357 Palm DAla DPhe NH₂ 86 457.31 358 Palm DAla DTrp NH₂ 85 473.33 359 Palm DAla DArg NH₂ 36 512.34 360 Palm DAla DHis NH₂ 96 482.36

Except for 35 members of the bank (shown in grey), all compounds were detected by a CL/SM ES+ analysis. The average purity determined based on the percent of the area of the expected peak detected at 214 nm on the chromatogram is greater than 83%.

EXAMPLE 2 Biological Properties of Five Dipeptide Conjugates According to this Invention

Experiments on inhibition of AMPc production were carried out on the M4Be human cell line with a concentration of 5×10⁻⁸ M of α-MSH. Five Palm-dipeptides according to this invention were introduced at different concentrations and each measurement was made in triplicate. Two or three series of experiments were made.

The tests were made as follows:

The M4Be human cell line (Jacubovich et al. Cancer Immunol. Immunother. 1979, 7, 59-64), a melanocytes cell line capable of producing melanines, was used in this study to determine the values of CI₅₀.

The cells were maintained in the Dulbecco modified Eagle medium with 10% of foetal calf serum (FCS), 1 mM of glutamine, 100 U/ml of penicillin and 10⁻⁴ g/ml of streptomycine.

All cell lines were maintained at 37° C. in an atmosphere with 5% of CO₂ and cell culture media were renewed every two days. The cells were applied in contact with a plate with 96 wells (Nunc, Roskilde) 24 hours before contact of dipeptides according to the invention.

AMPc was measured as follows:

Cells applied in contact the day before with 8×10⁴ cells per well were put in the presence of one of the five dipeptide conjugates according to the invention at various concentrations for 10 minutes at 37° C. with 5×10⁻⁸ M of α-MSH. After this time, the lysis of the cells was made and the AMPc content was measured using a connection test box by competition (RPN225, Amersham Pharmacia Biotech). Each independent experiment was carried out at least twice in triplicate.

The peptidic activity was determined with reference to the AMPc content synthesized by untreated cells and the production of AMPc induced by α-MSH alone. The curves were adjusted and the values of CI₅₀ were determined with non-linear regression in the GraphPad Prism (GraphPad software, San Diego, Calif., United States).

Table 2 below contains the results.

TABLE 2 Experiments on inhibition of AMPc production on M4Be cells CI50 CI50 CI50 CI50 Purity (μM) (μM) (μM) (μM) Compound Sequence (%) exp1 exp2 exp3 aver. 39 Palm-Arg-His-NH₂ 94 29 4.6 4.4 13 41 Palm-Arg-Arg-NH₂ 100 36 17 — 26 49 Palm-Arg-Pro-NH₂ 87 20 26 — 23 50 Palm-Arg-Lys-NH₂ 100 48 9.6 — 29 125 Palm-Ser-Pro-NH₂ 100 45 5.5 1.0 17

Thus, unexpectedly, the tested Palm-dipeptides appeared to be antagonists of the human MC₁ receptor of melanocortine using M4Be melanoma cell lines. These dipeptide conjugates have a CI₅₀ within a micromolar range. These dipeptides are the first example of short synthesis antagonist compounds binding to the MC₁ receptor and they open up the field for small molecule non-peptidic antagonists of α-MSH.

In particular, these compounds comprise an arginine residue in position AA2. Interestingly, compound 125 (Palm-Ser-Pro-NH₂) does not have any basic residue in its sequence, and has a value of CI₅₀ equal to 17 μM. This result showed that the bond to the MC₁ receptor does not necessarily require a positively charged radical.

With only two amino acid residues, these palmitoyled compounds can be considered as being leader compounds useful for design of non-peptide antagonists of α-MSH. 

1. Dipeptide conjugate with general formula I below: A-AA2-AA1-NH₂  I in which A represents the radical corresponding to palmitic acid, AA1 and AA2 represent identical or different amino acids selected from the group consisting of Pro, Arg, His, Lys, the corresponding homo-amino acids, and the corresponding beta-amino acids, in the form of enantiomers or diastereoisomers and mixtures thereof including racemic mixtures, with the proviso that at least one of the amino acids AA2 or AA1 is Arg and with the exception of the dipeptide conjugates Palm-Orn-Arg-NH₂ and Palm-Arg-Arg-NH₂.
 2. Dipeptide conjugate according to claim 1, wherein AA2 represents a basic amino acid.
 3. Dipeptide conjugate according to claim 1 wherein it is selected from among the group consisting of: a) A-Arg-His-NH₂, b) A-Arg-Pro-NH₂, and c) A-Arg-Lys-NH₂, in which the definition of A is as given in claim
 1. 4. Dipeptide conjugate according to claim 1, wherein it is selected from among the group consisting of 39) Palm-Arg-His-NH₂, 49) Palm-Arg-Pro-NH₂, and 50) Palm-Arg-Lys-NH₂.
 5. Cosmetic or pharmaceutical composition comprising a dipeptide conjugate according to claim 1, and possibly a cosmetically or pharmaceutically acceptable excipient.
 6. Method for lightening or whitening the epidermis, for eliminating skin spots, or for preventing pigmentation of the epidermis comprising the administration of an effective amount of a cosmetic composition according to claim 5 or a cosmetic composition comprising the dipeptide Palm-Arg-Arg-NH₂ to a patient in need thereof.
 7. Method according to claim 6, wherein the cosmetic composition is applied onto the skin.
 8. Dipeptide conjugate according to claim 2, wherein AA2 is Arg.
 9. Dipeptide conjugate according to claim 6, wherein the skin spots are age spots or freckles. 